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THE ACID OPEN-HEARTH  PROCESS.                         183
SEO. Xd.—Quantitative calculations on acid slags,—The fore-' going results do not show the alteration in the amount o.f the slag during the operation. It is out of the question to weigh Hie cinder at different periods, but it is possible to approach the truth by the following method: The final slag, after tapping, is weighed. By subtracting from this weight the MnO produced by the addition of the recarburizer and the sand from the tap-hole and ladle-linings, the amount of slag which was in the furnace before tapping may be computed. Given the analysis of the slag at that time, it is easy to calculate the weight of its constituents, among which will be the manganese; if the ore contained none of this element, the amount which was present throughout the operation will be known; and since the percentage of manganese in the slag and in the metal can be determined, and the weight of the metal can be calculated for any stage of the work, all the data are at hand for a determination of the weight of the slag at any time.                _J
This process applied to the two groups of heats in Table X-B gives the results in Table X-C, where it is shown that although nearly twice as much pig-iron was added in Group II, as in Table X-A, the greater oxidizing power of the oil flame took care of this extra amount, the result being seen in the greater quantity of slag after melting. When the bath was thoroughly fluid, the oil flame still acted more powerfully, but was unable to burn the iron, since the metalloids furnished ample protection, and the increase in the weight of slag during oreing is no greater in one group than in the other. In Group I, 41 per cent, of the ore was reduced, while
TABLE X-C. Reduction of Ore.
	Group I.	Group II.
Subject.	Goal gas, pounds.	Oil gas, pounds.
Slag after tapping . . ......... ..... . . . •'. .	4050	6070
Slag after melting ............... ..     ...	2810	4690
Ore"added ...•." ..... ..... ...........	1020	860
FeO in ore added ......... . .........	648	686
FeO reduced during oreing ................	880	SIS
in Group II there was 45 per cent. These figures have no general significance, for, if the slag is viscous after melting, a certain amount of ore will be necessary to confer fluidity and will not be